genirq/matrix: Prevent allocation counter corruption

When irq_matrix_free() is called for an unallocated vector the
managed_allocated and total_allocated counters get out of sync with the
real state of the matrix. Later, when the last interrupt is freed, these
counters will underflow resulting in UINTMAX because the counters are
unsigned.

While this is certainly a problem of the calling code, this can be catched
in the allocator by checking the allocation bit for the to be freed vector
which simplifies debugging.

An example of the problem described above:
https://lore.kernel.org/lkml/20210318192819.636943062@linutronix.de/

Add the missing sanity check and emit a warning when it triggers.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210319111823.1105248-1-vkuznets@redhat.com

diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index 6f8b1d171cdc8efbe56a23fd2900721d6c697823..578596e41cb60731cdae15038e5ad0df03dd647c 100644 (file)
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -422,7 +422,9 @@ void irq_matrix_free(struct irq_matrix *m, unsigned int cpu,
        if (WARN_ON_ONCE(bit < m->alloc_start || bit >= m->alloc_end))
                return;
 
-       clear_bit(bit, cm->alloc_map);
+       if (WARN_ON_ONCE(!test_and_clear_bit(bit, cm->alloc_map)))
+               return;
+
        cm->allocated--;
        if(managed)
                cm->managed_allocated--;